# Controlling torque of single phase ac induction motor

Discussion in 'Electronic Basics' started by bg, Apr 22, 2005.

1. ### bgGuest

i have a dayton shaded pole single phase ac induction motor with
1/150HP, 3000 RPM, 230 V, 60 Hz frequency and Full Load Amps 0.24A . I
would like to know whether there is any equation for troque.(connecting
current/voltage with torque)

ThankYou

2. ### Hans-Bernhard BroekerGuest

[F'up2 c.a.e --- this would be even *more* off-topic in the
electronics newsgroup, I think.]

230 V at 0.24 A is 55 VA, or, assuming a cos(\phi) of 1 for the
moment, 55 Watt. That doesn't quite figure with your HP figure, I
think --- it's off by one order of magnitude. Should this beast
really have a phase angle of acos(0.1)==84 degrees?
Torque times angular velocity, just like force times linear velocity,
equals power. So:

M = P / \omega
= P / (2*\pi*f)

Using the 1/150 HP (or roughly 5 Watt), that gives us a torque of
0.013 Nm. Using the 55 VA, you get 0.146 Nm. I'll leave it to the
metrically challenged to convert that into strange units ;-)

3. ### john jardineGuest

For shaded pole motors "speed control" by means of ac voltage, is a bit of a
non starter but ... must admit to doing one for a customer last week .
Similar 55Watt shaded pole as yours (European 230Vac though) and attached to
a small ducted fan.
Motor sits there and buzzes at 10% voltage. Two fingers can hold the shaft
up to 50% voltage. Beyond that and upto 100% voltage, a passing resemblance
to speed control.
Would estimate something like a square law response. Eg, halve the voltage
and torque drops four times. (actually slighly better than this, say T
proportional to V^1.6).

Conversation with customer goes sort of ...
Me. Ye canna break the laws of physics.
Them. But the one you did for the big fan works well.
Me. Yes but that was technically crap and I explained this at the time.
Them. Never mind the physics, just give us a quote.

When will customers ever learn that BumbleBees are incapable of flying?.
regards
john